In the production of panels, many manufacturing processes are performed at different work stations. To assure that these operations produce results which are precise with respect to the panel and to each other, the panel must be precisely positioned with respect to a reference coordinate system at each work station. Methods and apparatus to accomplish panel positioning must be consistently precise and also accommodate and minimize the effects of dimensional variations that occur in the panel during manufacture due to expansion, contraction, shear and other material instabilities.
One class of existing techniques of aligning a panel with a work surface reference frame utilizes a plurality of slots cut into the panel which fit over locating pins located on the work surface at each work station. Two ways of implementing this technique are shown in FIGS. 1 and 2, respectively. In FIG. 1 locating slots 1, 2 and 3 are cut into panel 4. Slots 1, 2 and 3 fit over pins 5, 6 and 7 of the work surface 9 (shown in fragmented form). The two horizontal slots 1 and 3 control the vertical positioning and angular positioning of the panel, and the vertical slot 2 controls its horizontal positioning. Since slots 1, 2 and 3 are all located along one edge of panel 4, it is apparent that the panel reference frame is along that edge as shown by axes 11 and 12 with the origin located within slot 2. The axis 12 is a fixed axis which goes through a fixed point determined by pin 6.
It is preferable to have the reference frame origin at the center of the panel to minimize worst case registration errors that result from linear deformations of the panel that occur during its manufacturing processing. One technique of moving the reference frame origin to the center of the panel is to utilize slots located along all four edges, as disclosed in FIG. 2. Four slots 21, 22, 23 and 24 are located at the center of each edge of the panel 15. Slots 21, 22, 23 and 24 are positioned over pins 25, 26, 27 and 28 to locate the panel on a work surface 19. As shown in FIG. 2, the reference frame origin 17 is at the center of the panel and defined by the two intersecting axes 31 and 32. Hence, changes in linear dimensions of the panel are minimized in both orthogonal directions of the reference frame. However, shear deformation of the panel is not accommodated by this technique.
Another method of positioning panels on a work surface in register with a reference coordinate system utilizes locator devices which engage V shaped slots cut in the center of each of three edges of the panel and which are operative to force the fourth and remaining edge against an abutment locator pad. Such a scheme is disclosed in U.S. Pat. No. 4,255,077 issued to R. B. Smith, Mar. 10, 1981. In this arrangement, however, the reference axis is still related to one edge of the panel with the positioning of one edge of the panel against a fixed locator pad.
Another method of alignment of panels at a work station is disclosed by R. C. Colineau in U.S. Pat. No. 4,425,076 issued Jan. 10, 1984. In this arrangement two roller stops define a first axis, and a third roller stop defines an end point. A first pivot arm with a roller forces one edge of the panel against the first two roller stops, and then a second pivot arm with a roller forces the panel against the third roller stop. This arrangement locates the panel with respect to a reference frame origin located at one corner of the panel.
Yet another method of positioning and aligning panels is disclosed by J. J. Hodges in U.S. Pat. No. 4,092,783, issued June 6, 1978, which includes apparatus for engaging opposing corners of the panel with clamping devices with a controlled equidistant disposition of the clamps to both correctly orient and center the panel and securely clamp it in one operation. This orients the panel with respect to a central point and a diagonal line connecting diagonally opposite corners.
Because of dimensional changes that occur in circuit panels during manufacturing, it is desirable that the positional reference frame be a fixed point preferably at or near the center or centroid of the panel in order to minimize the effect of these dimensional changes in positioning the panel on a work surface. It is also desirable that the positioning operations and apparatus be operative to align one axis of the panel passing through the fixed point with a work surface reference axis line.